1. Field of the Invention
The present invention generally relates to a starter having an epicycle reduction gear. More particularly, the present invention relates to a starter for starting an internal combustion engine having an epicycle reduction gear.
2. Related Art
It is common for starters for internal combustion engines to have a one-way clutch, which prevents driving of a starter motor by the engine when the engine is started. Normally, the one-way clutch is directly connected to a pinion gear.
Japanese Utility Model Publication Laid-Open No. 52-19528 discloses a starter equipped with an epicycle reduction gear. In this document, the one-way clutch is disposed between the outer periphery of an internal gear in the epicycle reduction gear and the inner periphery of the casing encompassing the epicycle reduction gear. Because the epicycle reduction gear and the one-way clutch are integrally formed, the one-way clutch is protected by the casing of the epicycle reduction gear from external dust and contaminated water, which could otherwise cause problems to the one-way clutch. Therefore, no additional sealing member, such as a casing and an O-ring, is required to be provided to the one-way clutch. Such a device provides a simplified structure.
However, in this structure, the one-way clutch is also disposed at the exterior edge of the internal gear, which needs to have a large diameter in order to house an epicycle reduction gear. Therefore, it is inevitable that the outside diameter of the casing encompassing the one-way clutch, i.e., the external diameter of the epicycle reduction gear integrally formed with the one-way clutch, is quite large. Such a structural feature causes the following problems.
The internal gear composes a clutch inner member, and a clutch outer member, which are mounted on the outside of the internal gear through a clutch roller. However, as the clutch outer member is large in diameter, the total weight of the system is increased.
Recently, a starter has been proposed that includes a starter motor that may be driven at high speeds and is then decelerated by an epicycle reduction gear in order to reduce the size and weight of the starter while simultaneously increasing its torque. This type of high-speed starter motor has been downsized in diameter so as to reduce the inertial mass and increase the resistance to centrifugal force. Accordingly, if a starter motor having a small diameter is equipped with an epicycle reduction gear integrally formed with a one-way clutch having a large diameter, the portion of the epicycle reduction gear integrally formed with the one-way clutch forms a flange that adversely affects the starter motor.
It is generally accepted that a starter will have a cylindrical magnet switch disposed adjacent to the starter motor. In such an arrangement, the magnet switch is disposed adjacent to and at the outside of the flange-like epicycle reduction gear integrally formed with a one-way clutch. As a result, a space that is not filled, i.e. a void, is formed between the starter motor and the magnet switch, thus adversely affecting the compactness of the starter.
In this case, if the internal gear is made thinner, the mean diameter of the one-way clutch can be reduced by the reduced amount of thickness of the internal gear. However, this manner of reducing the thickness and the overall size is not recommended, as problems, such as decreases in transmission efficiency and degradation of durability of the starter, occur due to deformation of the internal gear.
Furthermore, when the clutch of such a starter is in overrun idling, because the circumferential speed of the internal gear used as the clutch inner member is high and the outside diameter of the internal gear is large, the distances of idle sliding of the clutch roller and clutch inner member increase, thus increasing the wear and tear on the clutch inner member.